Suspended ceiling construction and compression strut therefor

ABSTRACT

This invention comprises a suspended ceiling grid system having an adjustable compression strut installed between the grid members of the system and the building or construction superstructure which lies in a plane above the suspended ceiling. The adjustable compression strut stabilizes the ceiling system and prevents upward movement of the system such as might occur during a seismic shock or earthquake tremor. The compression strut comprises two co-axial, telescoping cylindrical strut members having a spring clip attached to the inner end of the inner strut member that allows the strut to be extended but not retracted. The compression strut is installed by simply holding it in position between the suspended ceiling grid and the superstructure and then extending the strut members until they are locked in place by the action of the spring clip.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to suspended ceiling grid systems, and, moreparticularly, to an adjustable compression strut adapted to be installedbetween the grid members of such a system to the superstructure above,thereby stabilizing the ceiling system and preventing upward movement,such as might be encountered during an earthquake.

2. The Prior Art

The use of a rigid member or assembly of members in a suspended ceilinggrid system for seismic protection is well known. Grid systems of thistype are comprised of a plurality of parallel, spaced main grid membersand usually include a plurality of cross grid members extendingtransversely between the main grid members. A plurality of grid openingsis thereby formed in which tiles may be supported. The grid membersgenerally are suspended from a conventional ceiling or an overheadsupport structure framework, either of which will hereinafter bereferred to as a "superstructure." Frequently, the grid is suspended bymeans of hanger wires. However, hanger wires afford no resistance toupward movement of the suspended ceiling system, and forces such asencountered during a seismic disturbance may cause injuries to roomoccupants and damage to the ceiling system and nearby structures due tosubstantially unrestrained vertical motion of the ceiling system.

Accordingly, in installations where seismic disturbances are a concern,it is known in the art to provide a substantially rigid, vertical strutextending between the superstructure and the grid runners and crossrunners below. Means have been provided for fixing the upper and lowerends of the strut to the superstructure and grid members, respectively.Also, the length of the strut should be adjustable, since thegrid-to-superstructure distance may vary in a particular installation,and since clearance will be needed for installation of the strut.

There are several important design criteria of seismically protectedsuspended ceiling structures: The range of adjustability should be asgreat as possible. Installation should be easy, particularly theadjustment of the length of the strut, yet the strut must be rigid withgood compressive strength. The length of the strut should not changeonce it is installed. The design should be compatible with a variety ofgrid member types. The struts should be of simple construction and easyto manufacture.

Various approaches have been taken to the design of such struts, asshown in the following representative United States Patents:

In U.S. Pat. No. 3,842,561, a strut is disclosed having an uppercylindrical member which telescopes into a hollow, square lower sleeve.A hanger wire passes inside the strut from the grid to thesuperstructure. The length of the strut is fixed by means of a set screwthreaded through the square sleeve.

U.S. Pat. Nos. 3,995,823 and 4,545,166 both show suspension deviceshaving support rods with C-shaped or V-shaped clamps for lengthadjustment.

U.S. Pat. No. 4,084,364 discloses a cylindrical strut with aspring-loaded clip at the lower end, the spring being contained withinthe tube. The clip attaches to the bulb of an inverted-tee grid member.By pushing down on the cylinder, the spring is compressed and the upperend of the strut can be brought into position against thesuperstructure. A suspension wire is installed near the strut toestablish the distance between the grid and the superstructure.

Each of the designs known in the prior art have fallen short in someimportant aspect such as adjustability, rigidity, ease of installation,or simplicity.

SUMMARY OF THE INVENTION

The present invention addresses the shortcomings of the prior art byproviding a suspended ceiling grid construction with a compression strutwhich is strong, rigid, easily installed, readily adjusted and locked,yet which is economically manufactured and assembled. According to apreferred embodiment of the idea, the strut comprises two, co-axial,telescoping cylindrical strut members with a one-way spring clipattached to the inner end of the inner strut member that allows thestructure to be extended but not contracted. In the preferredembodiment, the spring clip is a disk that is dished and notched withpetals so that it, and the inner strut member, may be pulled through theouter strut member with little resistance. When an attempt is made topush the spring clip back in to the outer strut member, however, theouter edges of the spring clip bite into the inner wall of the outerstrut member making retraction of the strut impossible.

The lower end of the strut may be fabricated to fit over a grid member,or, as in the disclosed preferred embodiment, fitted with an end plugsuitably shaped.

The strut of the invention is installed by simply holding it in positionbetween the grid and the superstructure then extending the two strutmembers. When the strut is the correct length, fitting tightly, thelength will be locked by the action of the spring clip.

Manufacture of the strut is made easier because close tolerances of thestrut member diameters are not required. Instead, a bushing and aflanged plug are used to provide smooth telescoping movement.

The strut of the invention may be installed with or without an adjacenthanger wire. When the strut is adjacent a hanger wire, the inventionprovides a clip which engages the hanger wire and the strut.

In an alternate embodiment, a coil spring is provided between the springclip and the end of the inner strut member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, elevational, perspective view of a suspendedceiling structure according to the invention;

FIG. 2 is a perspective view of a compression strut according to theinvention;

FIG. 3 is a side view of the strut according to FIG. 2 with portions cutaway and in axial cross-section;

FIGS. 4, 5 and 6 are front, side and lower end views, respectively, ofthe strut end plug shown in FIG. 3.

FIGS. 7 and 8 are top and side views, respectively, of the spring clipshown in FIG. 3;

FIGS. 9 and 10 are lower end and side views, respectively of the innerstrut member plug shown in FIG. 3;

FIG. 11 is a perspective view of a spring clip according to theinvention, illustrating the attachment of the clip to a hanger wire andan adjacent strut; and

FIG. 12 is a side, elevational view, with portions cut away, of thestrut according to the invention showing an alternate arrangement of thestrut having a helical spring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By way of disclosing a preferred embodiment of the invention, and not byway of limitation, there is shown in FIG. 1 a fragment of a suspendedceiling structure 10 installed below a superstructure S. In its generalorganization, the ceiling structure includes a grid comprising aplurality of inverted-tee-shaped runners 11 and cross runners 12, tiles13 supported in the openings of the grid, a plurality of hanger wires 14which are fixed at their upper and lower ends to the superstructure andthe grid, thus establishing the distance therebetween, and a pluralityof compression strut assemblies 15 at spaced lateral intervals. Forpurpose of illustration, three strut assemblies 15 are shown atrelatively close spacing. It should be understood, however, that in anactual installation the spacing between struts will be on the order oftwelve feet. Two of the struts assemblies 15 are shown adjacent hangerwires 14, while a third is shown without a hanger wire but with anattachment clip 17 for securing the upper end of the strut in the properposition against the superstructure.

Referring now additionally to FIG. 2, it may be seen that eachcompression strut assembly is generally an elongated, two-part,telescoping cylinder including an upper, or first, or outer strut member20, a lower, or second, or inner strut member 21, the outer diameter ofthe member 21 being somewhat smaller that the inner diameter of themember 20. At the lower end of the outer strut member 20 there isinserted a bushing 23 having a bore slightly larger than the outerdiameter of the inner strut member 21.

At the lower end of the inner strut member there is inserted a lower endplug 25 having a bifurcation adapted to engage the bulb 27 formed at thetop of the web of the grid runners 11 and cross runners 12. Near theupper end, the wall of the outer strut member 20 is provided with two,diametrically opposite holes 29. These holes receive the hooked ends of"wishbone" shaped top clips 30. As more fully described below, these topclips 30 encircle the hanger wires 14 and hold the compression strutassemblies 15 in adjacency with the hanger wires.

Referring to FIG. 3, further details of a compression strut assembly 15may be seen. The bushing 23 is flanged and extends some distance intothe end of the outer strut member 20 with a friction fit. At the upperand of the inner strut member 21 there is a flanged inner end plug 32friction fit therein. As shown in FIGS. 9 and 10, the inner end plug 32is generally cylindrical with a flange 33 at one end and an axial bore34. The flange 33 of the inner end plug has an outer diameter slightlysmaller than the inner diameter of the outer strut member 20. The closefit of the inner end plug flange 33 and the bushing 23 provide forsmooth telescopic movement of the strut assembly.

The lower end plug 25 is shown in FIGS. 4, 5 and 6, and has abifurcation comprising two legs 35 and 36 forming an opening 37 suitablyshaped and dimensioned to engage a ceiling grid runner or cross runner.The lower end plug has a flange 38 and an upper extent 39 appropriatefor a friction fit in the lower end of the inner strut member 21.

Referring again to FIG. 3, the inner end plug 32 at the upper, or inner,end of inner strut member 21 has a spring clip 40 attached thereto. Asshown in FIGS. 7 and 8, the spring clip 40, preferably made of springsteel, is substantially in the form of a disk, with six, evenly spaced,radial notches, or slots 41 cuts cut along its perimeter, therebyforming six "petals" 42. In the center of the spring clip 40 there is ahole 43. As best shown in FIG. 8, the spring clip 40 is dished. The word"dished" is intended herein to include the shape of a spring clip thatis initially flat, but takes on a concave or frustoconical shape by thebending of the petals when confined within the upper strut. The outerdiameter of the dished, but unflexed, spring clip 40 is slightly largerthan the inner diameter of the outer strut member 20.

Referring once more to FIG. 3, the spring clip 40 is fastened concaveupward to the upper end of the inner strut member 21 by means of ascrew, 45 passing through the hole 34 of the spring clip and into thebore of inner end plug 32. The screw also causes expansion of the innerplug, resulting in a tight friction fit of the inner plug in the innerstrut member. Because of the relative diameters of the spring clip 40and the outer strut member 20, the petals 42 of the spring clip areflexed inwardly with the outer edges of the spring clip pressed tightlyagainst the inner wall of the outer strut member 20. As a result of thisarrangement, the strut assembly may be axially extended by pulling thetwo members 20 and 21 apart; however, when the strut assembly is axiallycompressed, the edges of the spring clip bite into the inner wall of theouter strut member and prevent any telescopic contraction of the strutassembly.

In FIG. 11 there is shown a wire clip 30 used to position a strutassembly 15 adjacent a hanger wire. The wire clip 30 is made of a singlepiece of wire formed in a wishbone shape to include an intermediate loop52, and two diverging legs 53 having hook portions 54 at their ends. Thehook portions 54 are adapted to engage the holes 59 formed through thewall of the outer strut member 20.

FIG. 12 illustrates an alternate embodiment of the invention wherein ahelical spring 60 is used in the strut assembly 15. One end of thespring 60 is attached to the inner plug 32. The other end of the spring60 is attached to the spring clip 40' by means of an appropriateattachment device 61. This arrangement allows for a certain degree ofvertical movement of the ceiling construction. Furthermore, wheninstalled with the spring compressed, the strut will be able to lengthensomewhat to compensate for any shifting of the ceiling such as might becaused by loosening or stretching of the hanger wires, or by objectsbumping up against the grid.

Referring again to FIG. 1, it will be seen that a compression strut 15may be installed not adjacent to a hanger wire. This may be done with aceiling clip 17 such as is disclosed in U.S. Pat. No. 4,084,364. A clipof this type is fixed in place to the superstructure and has means forengaging the upper end of the strut assembly.

Installation of the ceiling system according to the invention is made asfollows: The compression strut assemblies 15 are fabricated inpredetermined nominal lengths appropriate to theceiling-to-superstructure distance and are delivered to the constructionsite in the retracted, or contracted, condition. The grid runners andcross runners are assembled and suspended from the superstructure in aconventional, well-known manner, usually with hanger wires. Next, alocation where a compression strut is desired is identified. If thelocation is adjacent a hanger wire 14, a wire clip 50 may now or laterbe looped around the hanger wire and the hook ends 54 of the wire clipengaged with the holes 29 near the upper end of the strut assembly. Thestrut assembly is held in approximate position while the upper and lowermembers 20, 21 are extended axially. As the strut nears its ultimatelength, the legs 35 and 36 of the lower end plug 25 are put in positionaround the bulb of the grid member below and the strut assembly isextended further to put the strut assembly in compression.Alternatively, the upper end of the strut assembly may engage an clipabove such as clip 17.

To simplify the above procedure to its essential terms, the strutassembly is merely held in position then lengthened as far as it willgo. The spring clip 40 automatically locks the length.

Suitable materials for practicing the invention include galvanized steelfor the strut members, spring steel for the spring clip, and moldedresins such as Delrin brand resin for the plugs and bushings.

Among other possible variations, the strut assembly may be constructedwith the outer strut member telescoping within the lower member, as isshown in FIG. 12. Instead of using a plug 25 in the lower end of theinner strut member 21, it is possible to form the end of the inner strutmember 21 itself to engage the suspended ceiling runners andcross-runners. Other variations and modifications to the preferredembodiment are possible without departing from the scope and spirit ofthe appended claims.

I claim:
 1. A suspended ceiling construction comprising:a plurality ofgrid members suspended below a superstructure; and at least onecompression strut assembly extending between said superstructure and oneof said grid members, said compression strut assembly comprisinganelongated, tubular outer strut member having an inner surface and anelongated inner strut member in axial, telescoping relationship withsaid outer strut member, a first end of said inner strut member disposedwithin said outer strut member; locking means fixed to the first end ofsaid inner strut member, said locking means engaging the inner surfaceof the outer strut member and allowing axial extension of thecompression strut assembly but preventing axial contraction thereof,said locking means comprising a resilient disk spring clip having edgesbiting into the inner surface of the outer strut member.
 2. Theconstruction of claim 1 wherein said disk is dished and formed withradial notches and petals, the outer edges of the petals pressingagainst the inner surface of the outer strut member.
 3. The constructionof claim 2 wherein said hanger wire clip means comprises a wishboneshaped wire having an intermediate loop for encircling the hanger wire,two divergent legs extending outwardly from said loop, and means at theends of said legs for engaging said compression strut assembly.
 4. Theconstruction of claim 1 wherein an outer end of the compression strutassembly includes means for engaging a grid member.
 5. The constructionof claim 4 wherein said means for engaging a grid member comprises anend plug having a bifurcation receiving the grid member.
 6. Theconstruction of claim 1 further comprising a helical spring disposedbetween the locking means and the first end of the inner strut member.7. The construction of claim 1 wherein said inner and outer strutmembers are cylindrical and further comprising a bushing inserted in thefirst end of said outer member, said bushing having an inner diameterslightly larger than the outer diameter of said second strut member, anda flanged plug inserted in the first end of the inner strut member, thediameter of the flange being slightly smaller that the inner diameter ofthe outer strut member.
 8. A compression strut assembly for the verticalstabilization of a suspended grid ceiling comprising:an elongated,tubular outer strut member having an inner surface and an elongatedinner strut member in axial, telescoping relationship with said outerstrut member, a first end of said inner member inserted into a first endof said outer member; locking means fixed to the first end of said innerstrut member allowing axial extension of the compression strut assemblybut preventing axial contraction, said locking means comprising aresilient disk spring clip having edges biting into the inner surface ofthe outer strut member.
 9. The construction of claim 8 wherein said diskis dished and formed with radial notches and petals, the outer edges ofthe petals pressing against the inner surface of the outer strut member.10. The construction of claim 8 wherein an outer end of the compressionstrut assembly includes means for engaging a grid member.
 11. Theconstruction of claim 10 wherein said means for engaging a grid membercomprises an end plug having a bifurcation adapted to receive the gridmember.
 12. The construction of claim 11 further comprising a helicalspring disposed between the locking means and the first end of the innerstrut member.
 13. The construction of claim 11 wherein said inner andouter strut members are cylindrical and further comprising a bushinginserted in the first end of said outer member, said bushing having aninner diameter slightly larger than the outer diameter of said secondstrut member, and a flanged plug inserted in the first end of the innerstrut member, the diameter of the flange being slightly smaller that theinner diameter of the outer strut member.
 14. A method for installing acompression strut in a suspended grid ceiling construction comprisingthe steps of:providing a compression strut assembly having inner andouter telescoping elongated members with means for allowing axialextension of the strut but not contraction, positioning the strutassembly vertically between the superstructure and a member of thesuspended grid, axially extending the strut assembly until it fitstightly between the superstructure and the grid member; and clipping thestrut assembly to an adjacent hanger wire.
 15. A suspended ceilingconstruction comprising:a plurality of grid members suspended below asuperstructure; at least one hanger wire extending from thesuperstructure to one of said grid members; and at least one compressionstrut assembly disposed adjacent said hanger wire extending between saidsuperstructure and one of said grid members, said compression strutcomprisingan elongated, tubular outer strut member having an innersurface and an elongated inner strut member in axial, telescopingrelationship with said outer strut member, a first end of said innerstrut member disposed within said outer strut member; and locking meansfixed to the first end of said inner strut member, said locking meansengaging the inner surface of the outer strut member and allowing axialextension of the compression strut assembly but preventing axialcontraction thereof; and a hanger wire clip means engaging said hangerwire and said compression strut assembly.